I've come to the point that I have to solve and simulate fresnel equations and I'd wish I could do it using Elmer, do you guys have an idea on how to work on it? Is there a proper equation or solver on Elmer that allows me to do it?

Using Elmer just to solve Fresnel equations is not feasible since they are not PDEs. However, you could solve electromagnetic wave equations between different materials to analyze complex reflection/transmission boundaries. The refractive index, n, is associated to the relative permittivity, eps_r, and relative permeability, mu_r, by n=sqrt(eps_r*mu_r). And the EM wave can be solved by EMWaveSolver, see test cases EMWave*.